Officials said up to 15 people were injured. Police said two of the injuries were serious, and those two were flown from Monadnock Community Hospital to another facility. NHBB officials said they were told the injuries were not life-threatening.

MCH said it received 13 patients. Six people were treated and released from the hospital.

The Peterborough police chief said the explosion happened on the first floor of the plant, and the windows were blown out.

Crews from more than a dozen towns, including about 100 firefighters, were dispatched to the scene. There was no smoke or flames showing from the building.

Eight ambulances were called to the area, and local hospitals were asked to stage for possible hazmat patients. Fire officials said there were chemicals in the building, but they didn't know what the chemicals were.

Drivers were asked to avoid Route 202, but it was open again by 6 p.m.

New Hampshire Ball Bearings cancelled first shift for Tuesday morning. Employees scheduled to arrive at 7 a.m. Tuesday were told by company officials that the facility will not be open in time.

They plan to make a decision about second shift on Tuesday morning.

NHBB manufactures precision bearings used in the aerospace industry, in the defense industry and for dental applications, among others. It was founded in 1946 in Peterborough and now has three manufacturing facilities across the country.

Photos: Explosion at Peterborough facility

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WMUR/Ray Brewer

At least 15 people were injured in a major explosion at New Hampshire Ball Bearings in Peterborough on Monday.